1. Field of the Invention
The present invention relates to an organic electroluminescence element using organic emitting materials.
2. Description of the Related Art
There is a conventional display panel device using an organic electroluminescence element (also referred to herein as an organic EL element) with a predetermined pattern as shown in FIG. 11B. FIGS. 11A and 11B show a main structure of the conventional organic EL element. FIG. 11A shows a schematic cross-sectional view of the organic EL element. FIG. 11B shows a plane view of an example of an anode of indium-tin oxide (ITO) with a predetermined pattern formed on the substrate of the conventional organic EL element.
As shown in FIG. 11A, the organic EL element includes a light-permeable anode (ITO) 102 formed on a substrate 101 made of light-permeable material such as glass which has the pattern as shown in FIG. 11B. In the organic EL element, an organic emitting material layer 103 and a cathode 104 are layered in turn on the anode (ITO) 102. Upon application of a predetermined voltage across the anode 102 and the cathode 104 to allow a forward current to flow through the organic emitting material layer 103, the organic emitting material layer 103 partially emits with the corresponding pattern to the portion sandwiched by the anode (ITO) 102 and the cathode 104 in which the forward current flowing in the portion of the anode (ITO) 102.
On the other hand, since the anode and the substrate are different in their material from each other. The reflectivities, transmissivities and refractive indexes are not equivalent, so that the edge profile of the anode pattern is visible through the substrate in the conventional organic EL element, even though there is non-application of voltage between both electrodes. Namely, anyone visibly recognizes the pattern to be displayed on the display panel without respect to application of voltage between both electrodes or not.
In addition, there is a display panel comprising organic EL elements each including an organic emitting material layer are arranged as minute pixels in a matrix pattern in which the pixels are partially driven in response to a necessary pattern to be displayed so that various patterns may be displayed on the panel. In such display panel, all of the pixels are visible although there is no application of voltage between both electrodes. Furthermore, even when driving the display panel, anyone recognizes the edge profiles of the pixel pattern.
To take steps against such a problem of the ITO anode, a light-permeable material with a low transmissivity may be used for the substrate so as to make a uniform mask on the pattern or pixels during the non-emission. However, such a step decreases the emission efficiency of the element and reduces a display quality of the panel.